Fluorine-containing elastomers, particularly perfluoroelastomers mainly comprising a tetrafluoroethylene (TFE) unit are widely used as sealing materials, etc. to be used under harsh environment because excellent chemical resistance, solvent resistance and heat resistance are exhibited.
However, with advances in technologies, more rigorous demand for characteristics have been imposed, and in the fields of aviation and space industries, semiconductor manufacturing equipment and chemical plant, sealing property in vacuo, plasma resistance and heat resistance are demanded.
To cope with such a demand, perfluoroelastomer copolymers comprising TFE unit, perfluoro(methyl vinyl ether) (PMVE) unit and cyano group-containing monomer unit are used, but these copolymers have a high glass transition temperature Tg, is fragile at low temperature and have a problem with cold resistance.
Also, to cope with such a demand, there are used vinyl ethers having a long side chain in addition to vinyl ethers having a short side chain such as PMVE.
For example, in JP61-223007A and JP62-89713A, there are disclosed fluoroelastomers comprising a TFE unit and a monomer unit comprising CF2═CFO(CF2CFXO)mRf (X is a fluorine atom or a trifluoromethyl group; “m” is an integer of 1 to 5; Rf is a perfluoroalkyl group having 1 to 6 carbon atoms). However, since the fluoroelastomers comprise an iodine-containing monomer unit to impart crosslinkability, there is a problem that heat resistance of a crosslinked structure is low and heat resistance of a molded article is not good.
In WO 00/22002, there is disclosed a fluorine-containing polymer comprising a TFE unit and a monomer unit comprising CF2═CFORf (Rf is a perfluoroalkyl group having 1 to 5 carbon atoms or a perfluoroalkyl (poly)vinyl ether having 1 to 3 oxygen atoms and 3 to carbon atoms). However, since the polymer comprises an iodine-containing monomer unit to impart crosslinkability, there is room for improvement in that heat resistance of a crosslinked structure is low and heat resistance of a molded article is not good.
In JP9-291122A, there is disclosed a fluorine-containing copolymer elastomer comprising a TFE unit, perfluoro(vinyl ether) represented by CF2═CFO(CF2)2(OCF2)nOCF3 (“n” is an integer of 1 to 5) and a bromine-containing unsaturated monomer compound. The fluorine-containing copolymer elastomer has bromine atoms as a crosslinkable group, and has a problem that heat resistance of a crosslinked structure thereof is low and heat resistance of a molded article is not good.
In JP2001-354719A and JP2003-137930A, there are disclosed fluoroelastomers comprising a TFE unit and CF2═CFOCF2OR (R is a linear or branched C2 to C6 perfluoroalkyl group, a cyclic C5 to C6 perfluoroalkyl group or a linear or branched C2 to C6 perfluorooxyalkyl group having 1 to 3 oxygen atoms). JP2001-354719A and JP2003-137930A describe that it is preferable to have, as a cure site, iodine atom and/or bromine atom in a polymer chain and/or at an end of a polymer chain. However, in the case of having, as a cure site, iodine atom and/or bromine atom, there is a problem that heat resistance of a crosslinked structure is low and heat resistance of a molded article is not good.
In WO 2006/068685, there are disclosed fluoro polymers comprising a TFE unit and a monomer unit comprising CF2═CFORf2 (Rf2 is a perhaloalkyl group or a perhaloalkoxyalkyl group), and examples of the CF2═CFORf2 disclosed therein are CF2═CFOCF3, CF2═CFOCF2OCF2CF2CF3, CF2═CFOCF2OCF2CF3, CF2═CFOCF2OCF3, CF2═CFO(CF2)3OCF3, and CF2═CFOCF2CF2OCF3. The cure site of the fluoro polymers is amidoxime or amidrazone, and these cure sites have a problem in that a step of modifying a polymer is complicated.
In JP2002-507640A, there is disclosed a perfluoroelastomer comprising TFE as perfluoro olefin, perfluoroalkoxy vinyl ether and a cure site component having halogen group being capable of participating in peroxide crosslinking reaction. In the perfluoroelastomer, the cure site is formed by imparting halogen atom, and such a cure site has a problem that heat resistance of a crosslinked structure is low and heat resistance of a molded article is not good.
With respect to an elastomer composition comprising a monomer unit having nitrile group as a cure site, for example, JP10-237130A discloses a copolymer comprising, as a monomer, fluorine-containing nitrile compound represented by CH2═CFCF2O—(CF2O)x—(CF2CF2O)y—(CF2CF2O)z—(CF(CF3)CF2O)w—CF2CN (“x”, “y”, “z” and “w” independently represent 0 or an integer of 1 to 20, and the sum of “x”, “y”, “z” and “w” does not exceed 20). Since the fluorine-containing nitrile compound is not a perfluoro monomer but a fluoro monomer, there is a problem that polymerizability is not good and sufficient heat resistance cannot be obtained.
In WO 2006/068735, a monomer unit having nitrile group as a cure site is described. However, perfluoro vinyl ether is an allyl ether type perfluoro vinyl ether such as CF2═CF—CF(Z)—O—Rf, and when such a perfluoro allyl ether is used as a monomer unit, there is a problem that polymerizability is not good.
In JP2003-526705A, there is disclosed a fluoroelastomer comprising perfluoroolefin, perfluoro(alkoxy vinyl)ether and a copolymer unit derived from a cure site component being capable of participating in peroxide curing reaction, and TFE is disclosed as an example of perfluoroolefin, and CF2═CFOCF2OCF2CF2CF3, CF2═CFOCF2CF3, CF2═CFO(CF2)3OCF3, and CF2═CFOCF2CF2OCF3 are disclosed as examples of perfluoro(alkoxy vinyl)ether. Examples of the cure site component disclosed therein are iodine- or bromine-containing unsaturated monoolefin, CF2═CFO(CF2)nCN, CF2═CFO[CF2CFCF3O]pCF2CF(CF3)mCN and CF2═CF[OCF2CFCF3]xO(CF2)mCN. Curing reaction of this fluoroelastomer is peroxide curing reaction, and there is a problem that heat resistance of a crosslinked structure is low and heat resistance of a molded article is low.
In WO 2003/051987, there is disclosed a fluorine-containing elastomer comprising TFE as perfluoroolefin and CF2═CFORf (Rf is a perfluoroalkyl group having 1 to 8 carbon atoms or a fluoropolyoxyalkyl group having 1 to 20 carbon atoms) as perfluoro vinyl ether and having carboxyl group, alkoxycarbonyl group or nitrile group as a crosslinkable group. However, the fluorine-containing elastomer actually used is one having a perfluoro(methyl vinyl ether) unit, and there is room for improvement in cold resistance.